An inkjet printer forms an image on a print medium by placing a pattern of dots on the medium. Possible dot locations are represented by an array or grid of pixels that are arranged in a rectilinear array of rows and columns. The center-to-center distance between pixels, or dot pitch, is determined by the resolution of the printer. For example, for a printer capable of printing 300 dots per inch (dpi), the dot pitch of the array is 1/300 of an inch.
The quality of printed images produced by an inkjet printer depends in part on the resolution of the printer. Typically, higher or finer resolutions, where the printed dots are more closely spaced, results in higher quality images. Increasing the resolution of an inkjet printer increases the number of dots to be printed in a unit area by the product of the increase factor in each dimension in the grid. For example, doubling the print resolution from 300 to 600 dpi in a square grid results in four times as many dots per unit area. Consequently, without a decrease in dot size, four times as much ink would be printed in the same area. If too much ink is printed in a given area, the print medium can become saturated. Ink saturation can cause smudging and wrinkling of the medium.
One way to avoid saturating a print medium when printing dots that are larger than optimal for the grid resolution is to reduce the size of each dot. However, significant reductions in dot size may be extremely difficult, if not impractical, to achieve.
Addressing and placing a dot of ink at every pixel location in a high-resolution grid requires many redundant nozzles, very slow print head travel across the medium, or very high firing frequency. With each of these options there is either increased cost, slowed performance, or difficult technical challenges.
Therefore a method of printing is needed that provides high-resolution printing using a dot size that is larger than optimal for the grid resolution, while avoiding ink saturation of the print medium.
Further, true high-resolution printing involves large amounts of image data. For example, 1200.times.1200 dpi printing involves four times as much data as 600.times.600 dpi printing. The standard parallel port interface between a host computer and a printer can become a data bottleneck when transferring high-resolution print data to the printer. Faster and more efficient methods of transferring print data from the host computer to the printer are needed.